Prophylactic vaccinations are hailed as a miracle of modern medicine, the efficacy of a given vaccine, however, varies with the formulated antigenic context it contains. Unlike small-molecule drugs, vaccines are made of diverse materials, including proteins, polysaccharides, DNA, viruses, virus-like particles, irradiated live cells, synthetic peptides, and attenuated live organisms (viruses, bacteria, or parasites). In general, vaccines composed of antigenic proteins or their subunits are less immunogenic than ‘traditional vaccines’ (inactivated pathogens), so that they are often fortified with adjuvants such as aluminum, oligonucleotides (CpG DNA sequences), oil emulsions (MF59), and saponin-based mixtures (QS-21 and ISCOMATRIX). The clinical use of some adjuvants, for example aluminum, has however raised some safety concerns. Safer and more-effective adjuvants are constantly being searched for in contemporary vaccine development.
To date, three kinds of JEV vaccines exist, all of which possess some adverse effects as reported from time to time. For example, an imbalance in the immune system can be provoked when formalin-inactivated vaccines are used against measles or respiratory syncytial virus. Incomplete inactivation by formaldehyde was condemned for being incapable of controlling outbreaks of Venezuelan equine encephalitis and foot and mouth disease. Hence, suitable and effective inactivating agents are urgently needed to avoid repeating: such unfortunate incidences.
Antimicrobial peptides (AMPs) are a family of short cationic peptides synthesized and released by a wide variety of organisms. Recently, a synthetic adjuvant termed IC31 (composed of the antimicrobial peptide, KLKL5KLK, and deoxy-inosine/deoxy-cytosine (ODN1a)) was revealed to be able to satisfactorily induce antigen-specific Th1 cellular and humoral immune responses. Plus, a DNA vaccine in conjunction with the synthetic KLKL5KLK AMP was also reported to have good efficacy against Mycobacterium tuberculosis infections. Although several hundred AMPs have been identified, only a few of their roles in host immunity have been studied.